Obesity weighs on brain function, too

Obesity promotes diabetes, heart disease, high blood pressure and other maladies associated with increasing aging. • Excess weight may damage thinking, reasoning and memory as well, possibly by eroding the fatty insulation around the fibers that connect regions of the brain. • Losing weight through bariatric surgery, however, appears to restore at least some cognitive function, according to John Gunstad, a neuropsychologist at Kent State University in Ohio.

On average they performed on the low end of normal, although scores on memory and learning tests were in the impaired range for about 25 percent of participants, he and his colleagues reported in a recent article in the journal Surgery for Obesity and Related Diseases.

Twelve weeks later, however, the 109 patients who had undergone bariatric surgery and shed about 50 pounds scored within the average or above-average range for all cognitive tests. Those who didn't have surgery scored worse.

What made the difference? The change occurred not in brain cells themselves, but in the myelin — the fatty white insulation around the "wires" that connect brain cells, Gunstad believes.

This "white matter," as it is known, facilitates the transmission of signals between brain cells and brain regions.

The thicker and more robust the white matter, the faster and more reliably signals travel. Anything that damages myelin or causes it to thin, such as multiple sclerosis or aging, can disrupt brain functions.

In a study published last year in Obesity, Gunstad and his colleagues determined that as weight increases, the integrity of the myelin decreases, which could account for deficits in thinking and memory.

"Other research has linked obesity to white matter changes," he said. "Our research is the first to suggest that these changes can occur before the onset of more severe pathology. That's worrisome because subtle changes might be happening in the background in otherwise healthy people."

Gunstad began to suspect that obesity contributed to mental decline when he worked with older people in a large study.

Obese patients seemed to have mental difficulties more often than nonobese people. "I saw that obese patients had problems linked with attention, concentration, problem solving, and so on — all problems that have been linked to white matter changes," he said.

Although he can't explain the specific mechanism that causes mental decline, Gunstad thinks that obesity damages the brain in a number of ways.

"For example," he said, "it could trigger inflammation, which could damage blood vessels, and perhaps the brain itself."

In a recent study in the Archives of Neurology, researchers found that people who have insulin resistance — a condition that reduces the ability of cells, including brain cells, to utilize glucose for fuel — show some of the brain changes that precede Alzheimer's disease.

They concluded that even mild insulin resistance, which increases dramatically in people who are overweight and obese, can increase the risk of Alzheimer's.

Losing weight, however, makes the entire body, including the brain, more responsive to glucose, and therefore probably less susceptible to Alzheimer's and other forms of brain dysfunction, the researchers said.

Tom Valeo writes frequently about health matters. He can be reached at tom.valeo@gmail.com.